set peer certificate verification
*ctx, int (*callback)(X509_STORE_CTX *, void *),
sets the verification callback function for ctx.
SSL objects that are created from
ctx inherit the setting valid at the time when
SSL_new(3) is called.
Whenever a certificate is
verified during a SSL/TLS handshake, a verification function is called. If
the application does not explicitly specify a verification callback
function, the built-in verification function is used. If a verification
callback callback is specified via
the supplied callback function is called instead. By setting
NULL, the default
behaviour is restored.
When the verification must be performed,
callback will be called with the arguments
*x509_store_ctx, void *arg). The argument
arg is specified by the application when setting
callback should return 1 to indicate
verification success and 0 to indicate verification failure. If
SSL_VERIFY_PEER is set and
callback returns 0, the handshake will fail. As the
verification procedure may allow the connection to continue in case of
failure (by always returning 1) the verification result must be set in any
case using the error member of
x509_store_ctx so that the calling application will be
informed about the detailed result of the verification procedure!
Within x509_store_ctx, callback has access to the verify_callback function set using SSL_CTX_set_verify(3).
ssl(3), SSL_CTX_load_verify_locations(3), SSL_CTX_set_verify(3), SSL_get_verify_result(3)
appeared in SSLeay 0.6.1 and has been available since
Previous to OpenSSL 0.9.7, the arg argument
SSL_CTX_set_cert_verify_callback() was ignored,
and callback was called simply as
To compile software written for previous versions of OpenSSL, a dummy
argument will have to be added to callback.
Do not mix the verification callback described in this function with the verify_callback function called during the verification process. The latter is set using the SSL_CTX_set_verify(3) family of functions.
Providing a complete verification procedure including certificate purpose settings, etc., is a complex task. The built-in procedure is quite powerful and in most cases it should be sufficient to modify its behaviour using the verify_callback function.
not provide diagnostic information.